Oops! Didn't see this one before it got translated...
Salihinal is right - the Dutch was incomplete. A complete sentence would be 'Ik denk dat je (...) vergeten bent. Therefor, I think the translation should be 'I think you have forgotten' or 'I think you forgot'.
I'm sorry it had escaped my notice until now! I have just corrected the Dutch version so maybe Gamine or Lilan could correct the English one?